Processes are known which utilize fluidized bed techniques wherein a bed of a particulate solid, or solids, for conducting various interactions and/or reactions is contacted with upflow gases the velocity of which exceeds the minimum fluidization velocity, and which may even exceed the free fall velocities of the individual particles causing bed expansion and fluidization of the particles without sweeping significant amounts of the particles from the bed. Fluidized beds are employed in many industrial applications which involve interactions or reactions between a gaseous phase and solid particles.
In a particularly important type of process, now under development, it is known, e.g., to produce synthesis gas (H.sub.2 +CO) from low molecular weight hydrocarbons, primarily methane, reacted in the presence of steam and oxygen at high temperatures within a fluidized bed of catalyst, typically nickel-on-alumina, or a mixture of catalyst and particulate solids diluent used to aid in controlling the heats of reaction. The combination of high temperature and presence of oxygen in such reaction however creates conditions which make careful control, stability, and steady state operation acutely necessary; however difficult. The surface of the particulate catalytic solids thus becomes sticky and tends to agglomerate, leading to lowered catalyst efficiency (lower conversion), and larger particles that are more difficult to fluidize; and/or the production of fine particles due to abrasive impacts and attrition with concomitant loss of catalyst from the reactor, and clogged lines. In some other fluidized bed operations, e.g., gas-phase polyethylene plant reactors, particles grow in size due to the polymerization reaction without any fluidization pathology taking place. Control for such operations is known, or required to maintain conditions so that the growing particles do not become sticky and agglomerate; and devices have been developed and used in the past, with varying degrees of success to maintain the operational stability of such fluidized bed operations.
In accordance with U.S. Pat. No. 5,435,972 to Daw and Hawk, e.g., differential pressure sensing devices have been employed as a means of sensing, and controlling fluid bed operations. Thus, a differential pressure sensing device utilizing a pair of pressure taps is located axially one tap above the other, or at different levels across a fluidized bed to obtain an analog signal. Daw and Hawk employ the analog signal with an electrical circuit and work in real time to control the feed gas velocity to the fluidized bed.
In accordance with U.S. Pat. No. 4,858,144, as in the control method of Daw and Hawk, supra, Marsaly et al likewise generate an analog signal representative of "the time varying pressure drop" across a "segment of the bed". They employ a differential pressure recording device, digitize the analog signal with an A/D board, collect the data in a PC, and thereafter use a Fast Fourier Transform of the data set to determine recognizable cyclical events present in the fluidized bed. Comparison is then made between a bed which is operating "properly" vis-a-vis one operating "improperly." Thus, if subsequent data sets examined by Fourier transform exhibit altered states and/or different cyclical events it is apparent that the nature of the fluidization process has changed. These changes are thus considered as indicators of fluidization "pathology"; a type of signature analysis as applied in rotating machinery development. Both Daw and Hawk and Marsaly et al offer processes for analysis of events marked by differential pressure fluctuations, but neither is very effective in tracking changes in particle size, or bubble size; properties which are closer to, and more directly related to variables which affect fluid bed operations; particularly syn gas operations, a process for the better control of which there is a pressing need.